Process for the seasoning of wood



Patented Dec. 2, 1924.

PATENT OFFISE.

ROLF THELEN, OF MADISON, WISCONSIN, DEDICATED, BY MESNE ASSIGNMENTS, TO THE CITIZENS OF THE UNITED STATES OF AMERICA.

PROCESS FOR THE SEASONING OF WOOD.

No Drawing.

Application filed October 24, 1923. Serial No. 670,440.

(FILED UNDER THE ACT OF MARCH 3, 1883, 22 STAT. L, 625.)

and the invention herein described and claimed may be used by the Government of the United States, its officers and employees, and by any person in the United States without the payment to me of any royalty thereon I hereby dedicate the same to the free use of the Government and the people of the United States.

My invention consists in an improved process for the seasoning of wood which can be used under ordinary atmospheric conditions of temperature and humidity as Well as in artificially controlled and regulated atmospheres such as those existing in the ordinary dry. kiln. This process consists essentially in completely coating the wood to be dried with a moisture retardant paint, enamel, or similar substance and then exposing said wood to a drying atmosphere of suitable temperature and humidity until the desired degree of dryness is reached.

The art of seasoning wood consists principally in the removal of most of the moisture contained in the wood in its natural condition with the least possible deterioration of the Wood during the process. Many difficulties are encountered, most of which are due to the fact that the wood shrinks unevenly in drying and that it is necessary to' have the moisture at the surface of the wood less than that in the interior during the drying operation. This difierence in moisture is relied upon to produce transfusion of the moisture from the center to the surface, and is known as a moisture gradient. The steeper this gradient the more rapid will be the rate of transfusion of the moisture and the greater danger will there be of damage to the wood from the drying stresses which are set ,up by the uneven drying. These drying stresses can be kept at a minimum by keeping down the moisture graldient'. This obviously cuts down the drying rate, producing slower drying. This effect can be compensated for in some instances by the use of higher temperatures in the surrounding atmosphere, the higher temperatures increasing the ease with which the moisture can transfuse.

The most commonly employed method of controlling the moisture gradient is by controlling the humidity of'the atmosphere surrounding the wood being dried. A high humidity will reduce the moisture gradient and a low humidity will increase the moisture gradient. The use of high humidity retards the rate of evpaoration from the surface of the wood and the low humidity accelerates the rate of evaporation. Certain mechanical difliculties are experienced in maintaining the proper humidity in a dry kiln, it being necessary to provide special means of humidity control as well as an adequate circulation of air in the kiln. In the case of wood being air seasoned control of the humidity of the atmosphere surrounding the wood is practically impossible except to a certain extent in the case of wood being dried in sheds with adjustable means for regulating the ventilation.

It has been found when the wood is exposed to a definite temperature and humidity that the rate of evaporation of mois ture from the surface of wood and consequently the moisture gradient can be regulated within very wide limits by the use of suitable coatings such as paints, varnishes, enamels, para-fline, bituminous pitches, asvphaltic pitches, mixtures of rosin and lampblack and various other substances. In fact the use of some of these materials to prevent the very rapid drying out of the end surfaces of lumber which would normally take place is Well understood and in Wide commercial application. The object to be attained in this instance is to entirely arrest the evaporation from these surfaces. Recent experiments have shown that remarkably uniform drying can be accomplished if the entire surface of the wood be coated with a moisture-retarding coating which will permit a very slow rate of evaporation from the surfaces. This coating then serves to control the moistur gradient and makes unnecessary the control of the humidity of the atmosphere surrounding the wood being dried. By the use of a very impervious coating the moisture gradient Will be very small and the use of a less impervious coating will produce asteeper moisture gradient.

The method is especially adaptable to all conditions of air seasoning and kiln drying where the control of humidity is difiicult or impossible, and will find its greatest usefulness in the drying of thick stock of refractory species and material of irregular shape in which the exposure of end grain is not confined strictly to the ends of the pieces. In certain instances it may be desirable to coat the end grain of the wood to be dried with a coating which is more impervious than that applied to the side grain because the transfusion lengthwise of the grain is naturally much greater than that across the grain. This can readily be accomplished by the use of a thicker coating of the same material or by the use of more impervious coatings on the ends.

In actual operation the process is as folloWs: The wood to be dried is coated with the moisture-retardant coating by dipping, brushing, or other suitable means and after the coating is dry it is piled or arranged in such a manner that areasonably free circulation of air may be had around each piece. This may be accomplished in any one of numerous well-known methods. If the Mood is to be dried under atmospheric conditions of temperature and humidity it is desirable that it be protected from the sun and rain by means of a suitable roof or other covering. If it is to be dried at temperatures above normal as in a dry kiln, the manner of piling the individual pieces will be determined in large measure by the operating characteristics of the kiln. To give good results the kiln should have enough circulation of air to insure reasonable uniformity of temperaturethroughout the entire kiln. Since by this method a comparatively high temperature and low humidity can be maintained, the circulation problem becomes of little importance and practically any kind of kiln Will meet the requirements. The control of the humidity is not necessary since the coating controls the moisture gradient. All that is necessary is a reasonable control of the temperature in the kiln. Since the rate of evaporation is very small the normal leakage of air into and out of the kiln will be ample to remove the evaporated moisture. \Vhile certain coatings are more efficient tor the purpose intended than others, this inven tion is not limited specifically to any specified coating or coatings. Any coatin which fulfills the requirements may be usec.

Having fully described the principles of this invention, I claim as original:

The herein described process for the seasoning of wood, consisting of coating the wood to be dried with a moisture-retardant coating and then exposing said wood to a drying atmosphere.

October 8, 192a.

ROLF THELEN. 

